This invention relates to a pilot-operated double 4-way valve for controlling the flow of a relatively high pressure fluid from a single source to an extend port of either of a pair of cylinders with low pressure pilot fluid used for cylinder retraction.
The use of 4-way valves to control flow to one or more cylinders is known in the art. Such valves are normally only available for handling fluid pressures up to a value approximating 5,000 psi. A conventional type of 4-way valve with a valve spool will not operate reliably in a system where the fluid pressures may approximate 10,000 psi.
In overcoming the foregoing, this invention utilizes a pair of pilot controlled 3-way valves related to provide a 4-way valve, with selective delivery of high pressure fluid to either one of two cylinders for causing extension of a piston in the cylinder and with utilization of low pressure pilot fluid for retraction of a piston in a cylinder and maintenance of the pistons in the cylinders in retracted position.
The assignee of this application has, for many years, manufactured a 4-way valve having a pair of 3-way valve components and with positioning thereof under the control of a solenoid-operated pilot valve. This prior valve did not have a construction to provide for control of one or the other of a pair of cylinders by a pilot valve having pilot lines with pilot fluid also being used to retract pistons in the cylinders.
An additional prior construction of the assignee of this application is shown in the copending application referred to above, with a 4-way valve structure having a pair of 3-way valves associated with a single cylinder and with means for holding pressure. However, the pilot fluid was not directly utilized in conjunction with positioning of the piston of the cylinder.